Transition the compiler from GCC to Clang

[alanjian85]

Transitioning the compiler from GCC to Clang offers several advantages. These include smoother integration of the kernel with Rust userland and simplified compiler installation via package managers in major Linux distributions, rather than relying on a separate pre-compiled binary archive (such as carg-os/riscv-gnu-toolchain). It's important to note that any usage of GNU-specific features in the current implementation should be removed during this transition.

[alanjian85]

As the main repository is moved to carg-os/carg-os, this issue should be closed now.